<!doctype html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport"
          content="width=device-width, user-scalable=no, initial-scale=1.0, maximum-scale=1.0, minimum-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <script src="https://cdn.jsdelivr.net/npm/vue@2.6.10/dist/vue.js"></script>
    <title>Document</title>
</head>
<body>
    <div id="app">
        <input type="text" v-model="msg"/>

        <button @click="count++">累加count</button>
        doubleCount:{{doubleCount}}
    </div>
    <script>

        Vue.config.productionTip = false

        const vm = new Vue({
            el:'#app',
            data(){
                return{
                    msg:'',
                    count:2,
                }
            },
            computed:{
                doubleCount(){
                    return this.count * 2;
                }
            },

            watch:{
                msg(newVal,oldVal){
                    console.log('发送请求', newVal, oldVal)
                },
                doubleCount(){
                    console.log('重新计算count')
                }
            }
        })
    </script>
</body>
</html>